The present invention relates to an information storage system used for continuous recording of inputted information such as video information and audio information, and more particularly, to an information storage system that is improved in reliability for long-term operation to a large extent.
In recent years, with the development of communications networks including networks and digital broadcasts, digital delivery of information is coming into wider use. In such circumstance, an information storage system for recording the delivered information is playing a more important role. As a total quantity of delivered information increases, and as a quantity of information delivered per unit hour increases, the information storage system is required to achieve both high-volume recording and high-speed recording. As a most suitable data storage unit for those purposes, a magnetic disk device is commonly used. Conventionally, the magnetic disk device has been mainly used as a computer's outboard recorder. However, taking advantage of the characteristics described above, the magnetic disk device is coming into wider use as a recording medium in the field of home entertainment products, handling video and audio information.
Continuous delivery of digital information permits the digital information to be used in the following manner: recording the information continuously within a range of storage capacity of the information recording system; and utilizing only a desired portion of the recorded information at any time. Taking a digital broadcast as an example, recording a desired channel continuously while watching only a desired portion becomes possible. For example, the following convenient operations become possible: playing back a missed portion again; interrupting a program currently being watched, while a user leaves in the middle temporarily, and continuing watching the program with a time lag afterward; and watching a broadcast that has finished a few hours ago.
In this manner, as regards a recording system that uses a magnetic disk as an information recording medium, the following technology is disclosed in Japanese Patent Application 10-341389A: in an information storage system comprising a magnetic disk device and a magnetic tape device, information recorded on the magnetic disk device is backed up on the magnetic tape device at given time intervals; and in the event that a failure of the magnetic disk device occurs, the information is played back from the magnetic tape device.
In addition, in Japanese Patent Application 09-251353A, another information storage system is disclosed. To be more specific, in a disk-array type information storage system comprising a plurality of magnetic disk devices, reliability is increased by: keeping a reserve magnetic disk device in a stopped state; and in the event that a failure of the other magnetic disk occurs, switching to the reserve magnetic disk.
In Japanese Patent Application 08-194585A, another information storage system is disclosed. To be more specific, in an information storage system for video-on-demand system comprising a plurality of magnetic disk devices, reliability is increased by: striping video information into a plurality of magnetic disk devices to distribute and record the information; recording the same video information, of which a compression ratio is increased, on another magnetic disk device for backup; and in the event that a failure of the former magnetic disk devices is detected during retrieving, playing back only the information, which is recorded on the failed magnetic disk device, from the backup magnetic disk device.
In Japanese Patent Application 59-157870A, the following technology is disclosed: in an information storage system comprising a plurality of floppy-disk devices, reliability of each floppy-disk device is increased by driving only a floppy-disk device, which performs recording/retrieving operation, while keeping the other floppy-disk devices in a stopped state.
In Japanese Patent Application 08-190762A, the following information storage system is disclosed: in a disk-array type information storage system comprising a plurality of magnetic disk devices, reliability is increased by stopping rotations of the magnetic disk devices when information is not recorded/played back.
Concerning an information recording system for continuous recording, the data storage unit is perfectly in a state of continuous operation. The continuous operation is severest in use for almost all of the data storage units, from the viewpoint of reliability. Using a case of a magnetic disk device as an example, problems of reliability in the state of the continuous operation will be described as below.
The magnetic disk device mainly comprises a disk as a recording medium, a head for recording and retrieving on the disk, and a control circuit for recording and retrieving. The magnetic disk device further comprises a disk-rotation mechanism, a head-movement mechanism (actuator), and the like. Current magnetic disk devices generally perform recording and retrieving while flying the head above the disk with a fine gap. Concerning the magnetic disk devices currently on the market, flying distances are mainly 30 nm or less, which are extremely short. Generally, decreased reliability of the magnetic disk device is mainly caused by a damage of the head or the disk, resulting from direct contact of the head with the disk or from indirect contact through contamination or the like inside the device. If the flying distance decreases, and as a period during which the head is flying above the disk becomes longer, risk of a head or disk damage rapidly increases. In the state of the continuous operation during which recording operation is always performed, the head if is always flying above the disk. Therefore, an increase in operation time risks reliability furthermore acceleratively (tribological reliability). Moreover, in the state of the continuous operation, components of the mechanisms including the disk-rotation mechanism, the head-movement mechanism, and the like described above are also forced to operate continuously. As a result, a mechanical factor including for example wear-out of a bearing and the like also risks reliability furthermore (mechanical reliability).
However, in each of the conventional examples, there are not disclosed a recording method and an information storage system, which are capable of: increasing reliability of the recording system itself for continuous recording; and thereby avoiding a failure of the recording system for a long time.
It is desirable to provide an information storage system and method for continuous recording, capable of ensuring high reliability even when operating the information storage system continuously for a long time There is a need to minimize energy consumption in such a system during continuous operation. There is a further need to reduce heat production in such a system which is likely to occur during continuous operation. It is also desirable to reduce noise in such a system which can occur as a result of continuous operation.